Radio transmitter for obtaining course lines



July 8, 1941- J. GOLDMANN r-:AL v 2,248,752

RADIO TRANSMITTER FOR OBTAINING COURSE LINES Filed Feb. 4, 1939 2 Sheets-Shes?l 1 Fig. 1

v 6 l 7 3 F/L 'rae 70 Cmq/Ms July 8, 1941.

J. GOLDMANN ETAL RADIO TRANSMITTER FOR OBTAINING COURSE LINES Filed Feb, 4, 1939 2 Sheets-Sheet 2 Patented July 8, 1941 RADIO TRANSMITTER FOR OBTAINING COURSE LINES Joachim Goldmann, New York, N. Y., and Rudolf v. Ottenthal, Berlin, Germany, assignors to C. Lorenz Aktiengesellschaft, Berlin-Tempelhof, Lorenzweg, Germany, a company Application February 4, 1939, Serial N o. 254,586 In Germany February 4, 1938 (Cl. Z50- 11) 'i' Claims.

Transmitting arrangements for obtaining course lines are known, in which an antenna structure of predetermined directive property is combined with a second antenna structure which is continually fed from a high frequency generator. For instance, if in the simplest case a continually fed linear antenna is used which, as is well known, has a circular characteristic, and if further a directional antenna structure of double-circular directional characteristic is employed, then by combining the two alternately in a definite rhythm, such as the rhythm of the a-n or dot-dash method, and in accordance with phase coincidence and phase opposition, cardioidshaped radiation diagrams or patterns result which alternately overlap each other and by the point of intersection of which a course line is determined. According to the special purpose in each case the contiuously fed linear antenna is replaced by an antenna structure possessed of predetermined directive property in a manner not to produce cardioid-shaped patterns but clubshaped ones, for instance.

The invention is concerned with the mode of keying, that is, the phase reversal of the directive antenna structure arranged for cooperation with the continually fed antenna structure.

In order toeiect such phase reversal, the known methods of this kind employ a currentreversing switch or an arrangement of electron tubes which are alternately rendered eiective and ineffective. The arrangement of a reversing switch has the disadvantage that the entire high frequency power flows over .the contacts thereof. This arrangement is therefore only suitable in the case of small transmitting power. Another disadvantage due to the use of a reversing switch is that multi-polar contacts are to be switched here in a manner to open and close them all at exactly the same time, this being a requirement which, for constructional reasons, is difficult to fulll. As a result, during the keying operation load variations occur which act on the continuously fed antenna and in such manner that this antenna receives a power greater than otherwise, while at the receiving place a disturbing increase of loudness or a decrease thereof occur, whereby in the telephone the well-known cracking noise is heard.

To effect the keying by alternately opening and blocking electron tubes has the disadvantage that the construction of the tubes and their data affect the antenna phase and thereby the directional patterns.

In order to overcome these disadvantages, it

is proposed in accordance with the invention to obtain the said phase reversal by alternately short-circuiting and opening an arrangement of filter chains.

The arrangements as provided by the invention have the advantage that the switching operations are not effected in the energy flow. Another advantage is that only uni-polar contacts are necessary.

The invention further aims to avoid the load variations that otherwise arise through inaccuracies of switching. For this purpose suitable means, comprising filter chains, for instance, are interposed in the feed line for the antenna structure adapted to be keyed, namely, means the short-circuit resistance or no-load resistance of which constitutes such a load for the transmitter even during the transit time or reversal of the keying contacts that the current of the continuously fed antenna structure shall remain of the same amount. Another feature of the invention consists in constructing the filter chains after the manner of a bridge connection whose arms are alternately short-circuited and opened by means of a change-over contact, as will be understood from the following description, reference being had to the accompanying drawings which show two embodiments of the invention. In these drawings,

Fig. 1 illustrates the circuit arrangement of one embodiment, Fig. 2 is a wiring diagram of a detail adapted for use in connection with the arrangement represented in Fig. 1, Fig. 3 shows a circuit arrangement of the second embodiment, Fig. 4 represents the circuit arrangement of still another embodiment, while Figs. 5a and 5b are diagrams that serve to explain the function of arrangements according to Fig. 4.

In the arrangement shown in Fig. 1 a linear antenna l is continually fed from a high frequency generator 3 over a line 2. Superimposed upon the radiation of antenna I is the radiation of a directive antenna system composed of antennae li, 5. 'I'he phase reversal in the antenna system 4, 5 is effected in the following manner.

In accordance with the invention the power from generator 3 is alternately conducted by either one or the other of two current paths I, II connected in parallel. Both these paths are of the same line lag which, for instance, corresponds to a phase displacement of degrees. To such end lter chains 6, l, 3, 9 are included in the paths I, II. These paths are at their output end interconnected crosswise, in order that the phase of one such path shall be in opposition to that of the other path. The keying is effected by alternately opening and closing contacts I0, II. Whenever contact II is closed, while contact II) is open, as shown by way of example, the energy ows over the lter chains 6, 1 of path I. The filter chains have a Very high short-circuit resistance and a low no-load resistance. For instance, they will have this property if constructed in accordance with Fig. 2, being here each in the nature of a cross-connected member which is arranged for phase quadrature. If, however, contact II is closed, then at 8 and 9 the respective very high short-circuit resistances are eiective, path I thus not being affected. By opening contact II, while closing contact I0, its energy is caused to flow over path II, whereby in the antenna system 4, 5 the phase is reversed on account of the output lines of the lter chains being arranged crosswise. The surge impedances of the filter chains 6, 'I, I), 9 are proportioned in accordance with the appertaining interconnectors. If necessary, transformers may serve this purpose.

The arrangement according to Fig. 1 is based on the assumption that the contacts I0, II shall precisely operate one immediately after the other. However, this condition is difcult to fulfil. If not fulilled, the contacts III, II thus happening to be momentarily opened or closed Iboth at the same time, then the arrangement shown in Fig. 1

gives rise to a load variation which acts to impair the radiation of antenna I. In order to avoid this disadvantage, the arrangement represented in Fig. 3 may be adopted. Here the same reference characters are used as in Fig. 1, as far as possible.

For obviating the said load variation the arrangement shown in Fig. 3 has a iilter chain I2 which likewise has a Very high short-circuit resistance, while having a low no-load resistance. Whenever now the contacts ID, II happen to be momentarily closed both at the same time a high resistance is placed across the output of iilter I2. This condition would throw a large current into the system I4, I5, I6 if rilter I2 were not present.

However, the very high short-circuit resistance of the lter chains 6, 8 will influence filter chain I2 at the output end thereof to produce the noload condition thereof. This chain I2 hence acts as a low rio-load resistance since the high resistance causes it to operate as though it were substantially open circuted and thereby prevents the power from increasing in consequence of such inaccuracy of switching the contacts I0, I I. If, however, the contacts I, II are momentarily open both at the same time, the low no-load resistance of the filter chains 6, 8 will act on lilter chain I2 at the output end thereof, whereby this lter chain I2 will be of very high resistance. Thus the abnormal low resistance of the circuit would drain energy to reflectors 4, 5 in the abscence of filter chain I2. The device I2 is so dimensioned that its short-circuit resistance or noload resistance, as the case may -be in cooperation with lters 6 and 8, shall constitute such a load for antenna I during the reversal of the keying contacts that the radiation thereof will be invariably the same. In order to provide for suitably adjusting the phasal interrelation of the antennae 4, 5, an adjustable filter chain I3 may be arranged as shown in Fig. 3.

As represented in Fig. .3 by way of example, the continually fed antenna structure may Ibe a directional antenna system composed of radiators I4, I5, IE5 spaced apart by distances equal to M2, A being the operative wave length. However,

any other antenna structure may be arranged instead in accordance with special requirements.

In the arrangement represented in Fig. 4, the linear antenna I is likewise continually fed from high frequency generator 3 over line 2. On the radiation of antenna I the radiation of the directional antenna system composed of radiators 4, 5, for instance, is superimposed in phase coincidence and phase opposition alternately. The phase reversal in antenna system 4, 5 is in accordance with the invention effected by a bridge connection 6'.

This bridge connection lcomprises two equivalent inductances LI, L2, two equivalent capacities Cl, C2, and a capacity C3 which is of double the value of CI or C2. Generator 3 is connected with terminals I1, I8 of the bridge 6. Antenna system 4, 5 is joined to terminals I9, 20 thereof. The keying is effected with the aid of a change-over switch 2| which in its position a acts to shortcircuit the bridge arm shown on the left in Fig. 4, while in position b thereof `the bridge yarm located on the right-hand side in Fig. 4 is short-circuited, whereby the phase of the current owing into antenna system 4, 5 is turned by 180 degrees. The mid-position of switch 2I is designated c. Filter I2 is provided for equalizing energy fed to antenna I during reversal of the switch frame from a to b.

The advantage of the arrangement represented in Fig. 4 is that instead of a number of contacts difficult to adjust only a simple change-over contact is necessary for the described keying operation, this contact not requiring special adjustment.

The result obtained by this change-over operation is based in principle on the relation L being the inductance value of LI or L2, while C is the capacity value of CI or C2 or C3/2.

In Figs. 5a and 5b the lter chains rendered effective in accordance with the two switch positions a, b are represented. Fig. 5a corresponds to position a., while Fig. 5b corresponds to position b. The reference characters of Figs. 5a, 5b are, as far as possible, in accord with those of Figs. 1 to 4. As will appear from Fig. 4, the polarity of the output end of bridge 6 is alternately reversed by the operation of switch 2|, whereby the phase at the terminals I9, 20 is displaced in the rhythm of the switch operation, namely, displaced by ;t90 degrees with respect to the terminals I'I, I8. lIhe parallel resonant circuit comprising LI, CS/Z, Fig. 5a, or comprising L2, C3/2, Fig. 5b, has a resistance of innite magnitude and is hence ineffective in the case of parallel connection.

With the switch 2l in position c the bridge 6 owing to the relation is in its state of equilibrium. The terminals I'I, I8 are hence short-circuited by two circuits connected in parallel. As a result, no energy flows to antenna system 4, 5 as long as switch 2| is changing its position. Filter chain I2 during this interval causes antenna I Yto radiate with unaltered energy so that in the region of the guide beam no cracking noise will be heard. This is attributable to the fact that lter chain I2 acts to destroy the energy intended for antennae 4, 5,

this energy thus being prevented from reacting on antenna I.

What is claimed is:

1. A radio transmitter for obtaining course lines, which comprises a high frequency generator, an antenna structure connected to be continually fed by this generator, a directive antenna structure arranged for cooperation With this continually fed antenna structure, said directive antenna structure comprising a plurality of radiation units, transmission means for energizing said radiating units in phase displaced relation with respect to said antenna structure, lter chains in said transmission means, meansy for connecting said lter chains to said directive antenna structure to respectively energize said units in phase reversal relations, and means for alternately short circuiting one of said iilter chains and opening the other to reverse the phase conditions of said directive antenna structure.

2. A radio transmitter according to claim 1, wherein the lter chains have a high short-circuit resistance and a low no-load resistance.

3. A radio transmitter according to claim 1, wherein the filter chains each constitute crossconnected members.

4. A radio transmitter according to claim 1, in which the continually fed antenna structure has a predetermined directive property.

5. A radio transmitter according to claim 1, wherein the continually fed antenna structure comprises three dipoles spaced apart by distances equal to one half of the operative wave length.

6. A radio transmitter according to claim 1, in which the filter chains are comprised in a bridge connection and in which a change-over switch is employed for alternately short-circuiting and opening two arms of this bridge connection.

7. A radio transmitter according to claim 1, in which the filter chains are comprised in a bridge connection having two side arms and a third arm between these, and containing two equivalent inductances and two equivalent capacities in these side arms and a capacity in the said third arm, the latter capacity being double that of each of the two other said capacities, a change-over switch being employed for alternately short-circuiting and opening the two capacities located in the side arms of the bridge.

RUDOLFI1 V. OTTENTHAL. JOACHIM GOLDMANN. 

